I seem to recall that the "experts" went with a heavier bullet because of the expected increased range of combat in the Middle East.
I've also heard that the 55 grain bullet was designed to tumble on impact,....don't know if it's fact or not. I've seen tests in ballistic gelatin where the 55 grain bullet fragments at the cannelure.
One interesting aspect of the gelatin test was that the 55 grain bullet would create a large temporary expansion cavity that started almost immediately upon impact when it was traveling at around 3100 fps. But at lower velocities the expansion cavity would appear further back in the gelatin.
My takeaway from the test was, at 2700 fps or so, the bullet would just pencil through before it had an opportunity to disrupt. But a few hundred fps more, it would create a lot of disruption beginning at impact.
Maybe the lower velocities from heavier bullets/shorter barrels reduced the lethality of the 5.56?
,...just my ponderings on the subject. Maybe legit,....maybe not.
